The invention relates to a method for producing plastics containers from thermoplastics with inserts which, by exploiting the heat of plasticization, are connected during shaping of the plastics container by a material bond and/or interlocking connection to the container wall, wherein the method provides the use of at least one opening on the insert, which opening forms a melt duct or melt inlet and/or melt passage for plasticized or plastic material of the container wall, wherein the method is distinguished in that the opening is monitored as a reference opening by optical and/or sensory means during the production of the connection, wherein the degree of penetration of the opening with thermoplastic from the container wall is used as a measure of the quality of the connection.